Buffer pre-fill

[h3ndrik]

allow the user to pre-fill the AudioFileSourceBuffer before calling out.begin()

[h3ndrik]

i'm sorry, there is still some error.
with this patch applied, the decoder doesn't recover from decoding errors any more.
i can only imagine this is because before 'filled' was still false after the non-blocking fill() call and now length can become >0

[h3ndrik]

reverted that change and set filled after pre-buffering.

There is already a comment in the code about forcing a complete refill:

ESP8266Audio/src/AudioFileSourceBuffer.cpp

Line 132 in 428726e

// We're out of buffered data, need to force a complete refill. Thanks, @armSeb

That's probably why we don't only look at length;-) Sorry.

EDIT: Not sure if this is a real problem. I'm having the same problems after reverting that commit.
There is something wrong with the mad mp3 decoder losing sync and then not syncing ever again. Happens on some (most) of the internet streams and i'm not sure why it can't sync again.

EDIT2: Problem gone after changing ...ICY... to AudioFileSourceHTTPStream. I'll open another bug report for that.